1. Field of the Invention
The present invention relates to a gas blowing plug used for blowing gas to agitate molten metal in a ladle, electric furnace, converter, degassing apparatus, and the like.
2. Description of Related Art
Conventionally, in order to promote refining reaction of molten metal, especially molten steel contained in a ladle, gas blowing is often performed. As means for this purpose, a gas blowing plug is used. FIG. 8 shows a construction of a conventional plug. A well brick 4 is disposed among bottom bricks 5 disposed on the upper side of a permanent lining 6 at the bottom of a ladle. A porous plug 2 contained in a metal case 3 is inserted from the lower side of iron shell 7 of the ladle, is supported by a holding brick 8, which is fixed by a holding plug 10. Blowing gas is supplied through a gas pipe 12, and is blown into molten metal in the ladle through the porous plug 2.
The conventional plug is made of a highly permeable refractory material, and blows Ar or N2 gas to cause nonmetallic inclusion to float up or to make the temperature uniform. As the refractory material, alumina materials, magnesia materials, zircon materials, or the like are used. The permeability is approximately in the range of 0.5 to 8 cm3-cm/cm2-s-cmH2O.
However, since the permeability must be ensured to blow a large amount of gas, it is necessary to make the material have a low density, so that the life of plug is impaired. To increase the life, the material of brick must be made dense, therefore the permeability must be decreased. Hence, it is difficult to manufacture a desirable porous plug.
To solve this problem, for example, Unexamined Japanese Patent Publication No. 11-117014 has disclosed a method in which a hot-melt sheet is formed in a spiral form, and is embedded in a refractory material and fired to make a dense plug after melting the sheet with a spiral slit inside. However, after the plug is once used, molten metal intrudes in a spiral-form slit and solidifies, so that it is sometimes difficult to blow gas into the molten metal for the next turn.
In such a case, it is normally necessary to increase the gas pressure to blow off the clogged portion. Therefore, the plug is consumed by about 5 to 20 mm for each blowing-off operation, so that the life of porous plug is decreased. When the molten metal intrudes into the slit deeply, it is sometimes difficult to blow off this portion, and in some cases, gas cannot be blown.
Accordingly, the inventor of the present invention reached an idea that a plug provided with discontinuous shallow slits having a difference in height limits the intrusion depth of molten metal in the slits can solve the above problems, and consequently made the invention as described below.
The first embodiment of the present invention provides a gas blowing plug for blowing gas from the bottom of a molten metal vessel, comprising;
a slit-shaped gas passage ranging from the bottom to the top of said plug, which forms a continuous slit-shaped gas passage in the horizontal cross section of said plug;
said slit-shaped gas passage forming a continuous passage from the bottom to the top of said plug; and
a discontinuous slit-shaped gas passage in the vertical cross section of the plug.
The second embodiment of the present invention provides a gas blowing plug for blowing gas from the bottom of a molten metal vessel, comprising;
a slit-shaped gas passage ranging from the bottom to the top of said plug, which forms
a discontinuous slit-shaped gas passage in the horizontal cross section of said plug;
said slit-shaped gas passage continuous from the bottom to the top of said plug in the vertical cross section of the plug; and
a discontinuous slit-shaped gas passage in the vertical cross section of said plug.
The third embodiment of the present invention provides the gas blowing plug, wherein said slit-shaped gas passage is formed by a continuous or discontinuous slit-shaped gas passage having a star shape in the horizontal cross section of the plug.
The fourth embodiment of the present invention provides the gas blowing plug, wherein said star shape is any one shape of three-pointed, four-pointed, five-pointed, or six-pointed star.
The fifth embodiment of the present invention provides the gas blowing plug, wherein said slit-shaped gas passage is formed in a multiple or spiral form around the centerline of the horizontal cross section of said plug.
The sixth embodiment of the present invention provides a manufacturing method for a gas blowing plug, comprising the steps of:
(a) preparing a tubular body made of a plane-shaped combustible sheet, which is formed into a tubular shape, cuts are made at predetermined intervals in the direction perpendicular to the axial direction of said tubular body, and a band-shaped convex portion is formed by projecting the cut portion from the inside to the outside;
(b) disposing said tubular body in a mold, and filling the same with a monolithic refractory material; and
(c) compressing said monolithic refractory material and then sintering the same.
The seventh embodiment of the present invention provides the manufacturing method for a gas blowing plug, wherein said band-shaped convex portion formed by the cut of said tubular body is a convex portion having an inclined portion inclining downward at both ends thereof.
The eighth embodiment of the present invention provides the manufacturing method for a gas blowing plug, wherein said plane-shaped combustible sheet is formed by a paper or plastic sheet with a thickness of 0.1 to 0.4 mm.
The ninth embodiment of the present invention provides the manufacturing method for a gas blowing plug, wherein said tubular body has any shape of three-pointed star, four-pointed star, five-pointed star, six-pointed star, or spiral in the vertical cross section .
The tenth embodiment of the present invention provides the manufacturing method for a gas blowing plug, wherein said tubular body is formed by disposing one or more tubular bodies with a different cross-sectional diameter in a multiple or spiral form around the center of a mold for said plug.